Function generator



Dec. 22, 1964 M. A. MAc LAIN 3,162,333

FUNCTION GENERATOR Filed June 29, 1962 INVENTOR. MANUEL A.-MAC LAIN ATTORNEY United States Patent 3,162,833 FUNCTION GENERATOR Manuel A.-MacLain, Wiclditfe, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Filed June 29, 1962, Ser. No. 206,331 4 Claims. (Cl. 338-89) This invention relates to function generating devices and more particularly to an improved slidewire resistance having a characterized transfer function.

Heretofore variable resistance devices have been employed to produce a signal or electrical resistance having a desired mathematical relationship with a mechanical input. In general, however, such devices have been costly to manufacture and complex devices subject to mechanical failures.

It is a principal object of my invention to provide an improved variable resistance device having a transfer function which can be simply characterized in accordance with a desired mathematical equation.

Another object of the invention is to provide a simple low-cost means to characterize the output of a slidewire resistance.

In a preferred embodiment of the invention a slide wire resistance is provided with a movable housing containing a resistance element of predetermined length and a contact arm movable relative to said housing. An input motion positions the contact arm to vary the resistance and simultaneously positions a cam having a surface defining a predetermined characteristic. A cam follower engages said surface and is effective to position the slidewire housing to characterize the output of the slidewire resistance in accordance with the cam characteristic.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing which is a schematic illustration of a function generator embodying this invention.

Referring to the drawing, there is shown a slidewise resistance indicated generally by the reference numeral 10. The slidewire resistance comprises a hollow cylindrical housing 12 rotatably mounted on an elongated shaft 14 supported by a bearing assembly 15. A wire resistance element 16 is fixed to the inner peripheral surface of housing 12 and connected at one end to a terminal 24 by a conductor 26. A movable contact arm 22 electrically connected to a terminal 18 by a conductor 20 and engaging resistance element 16 is fixed to shaft 14 for rotation therewith relative to housing 12 and resistance element 16. It will be apparent that rotation of shaft 14 and contact arm 22 relative to housing 12 will vary the length of resistance element 16 connected across terminals 18 and 24. If housing 12 were fixed against rotation the change in resistance would be linear with respect to the angular displacement of shaft 14.

In accordance with the invention I arrange housing 12 to be positioned simultaneously with contact arm 22 in response to angular displacement of shaft 14, but relative thereto in accordance with a mathematical function to establish a resistance change across terminals 18 and 24 having a non-linear relationship with the position of shaft 14. To this end a cam 30 having a surface 32 engaged by a follower 34 is fixed to the shaft 14 to be rotated therewith. The surface 32 has a predetermined rise with angular displacement of the cam 30 to establish a predetermined mathematical relationship between the angular displacement of cam 30 and displacement of follower 34.

The follower 34 is carried on one end of a follower arm 36, the other end of which is fixed to one end of a shaft 38 rotatably supported in a bearing assembly 40. A pulley 42 is fixed to the other end of shaft 38 to be rotated thereby. The housing 12 of slidewire resistance 3,162,833 Patented Dec. 22, 1964 ice 10 is provided with a peripheral groove 44 in the exterior surface thereof which is aligned with the pulley 42. A drive cable 46 engages groove 44 and is driven by pulley 42 to effect angular displacement of housing 10 in response to angular displacement of pulley 42.

In operation of the system illustrated in the drawing, an angular displacement of shaft 14 :is effective to displace contact arm 22 relatively to the housing 12 and resistance element 16 and effective to rotate cam 30. Angular displacement of cam 30 will effect displacement of follower 34 and arm 36 causing an angular displacement of shaft 38 and pulley 42. Displacement of pulley 42 is transmitted by cable 46 to housing 12 to effect a corresponding angular displacement of resistance element 16. The displacement of contact arm 22 is directly proportional to the input angular displacement of shaft 14 while the displacement of housing 12 is determined by the characteristic of cam 30 and thus a mathematical function. Accordingly, the net displacement of contact arm 22 relative to resistance element 16 and thus the change in resistance between terminals 18 and 24 has a mathematical relationship to the input angular displacement of shaft 14 determined by the characteristic of cam 30. Thus, an angular displacement of shaft 14 produces a change in resistance related to the angular displacement by a desired mathematical function.

It will be apparent that by varying the characteristic of cam surface 32 any desired transfer function can be obtained. The surface 32 may be characterized for example to produce a square-root relationship between the angular displacement of shaft 14 and change in resistance across terminals 18 and 24, to provide a squareroot extracting device which would have utility in the measurement of a variable flow rate. For example if the angular displacement of shaft 14 were proportional to a differential pressure which varies with the square of a flow rate the resistance across terminals 18 and 24 would have a linear relationship to the flow rate.

The disclosed function generating device due to its simplicity in structure provides a convenient low-cost apparatus for producing a characterized transfer function. Thus, the objects of the invention have been accomplished.

While only one embodiment of the invention has been herein shown and described, it will be apparent to those skilled in the art that many changes may be made in the construction and arrangement of parts without departing from the scope of the invention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a function generator, the combination comprising, a rotatable shaft, a housing rotatably mounted on said shaft for movement relative thereto, a slidewire resistance fixed to said housing for movement therewith, a contact arm fixed to said shaft for rotation therewith relative to said resistance element to vary the effective length of said resistance element between one end thereof and said contact arm, a cam having a surface defining a predetermined characteristic fixed to said shaft for rotation therewith, a second rotatable shaft, an arm extending from said second shaft, a follower carried by said arm engaging said surface to effect angular displacement of said second shaft upon rotation of said cam, a driving pulley fixed to said second shaft and a driving cable for transmitting angular displacement of said driving pulley to said housing.

2. In a function generator as claimed in claim 1 wherein said housing is of generally cylindrical configuration having a groove in the peripheral surface thereof engaged by said driving cable.

3. In a function generator, the combination comprising, a first rotatable shaft, a variable impedance device including a pair of relatively movable parts, the impedance of said device varying in proportion to relative movement between said parts, a driving connection between said first shaft and one of said pair of parts to thereby produce relative movement between said parts as said first shaft is angularly positioned, a second rotatable shaft, a driving connection between said second shaft and the other part of said pair of parts to thereby produce relative movement between said pair of parts as said second shaft is angularly position, a non-linear cam secured to said first shaft for rotation there-with and a cam follower engaging said cam secured to said second shaft whereby said second shaft is angularly positioned in non-linear relationship to angular movement of said first shaft.

4. In a function generator for producing an output signal varying in non-linear relationship with an input signal, in combination, a first shaft adapted to be angularly positioned in direct proportion to changes in the input signal, a pair of relatively movable parts, the relative positions of said parts determining the magnitude of the output signal, one of said parts rotatably mounted on said shaft for movement relative thereto, the other of said parts fixed to said shaft for movement therewith to thereby produce relative movement of said parts as said shaft rotates, a second rotatable shaft, a driving connection between said second shaft and said one part to angularly position said one part about said first shaft to thereby produce relative movement between said parts a non-linear cam fixedly mounted on said first shaft and a cam follower fixedly mounted on said second shaft engaging said cam whereby said second shaft is angularly positioned in non-linear relationship to angular movement of said first shaft.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Nov. 20, 1957 

1. IN A FUNCTION GENERATOR, THE COMBINATION COMPRISING, A ROTATABLE SHAFT, A HOUSING ROTATABLY MOUNTED ON SAID SHAFT FOR MOVEMENT RELATIVE THERETO, A SLIDEWIRE RESISTANCE FIXED TO SAID HOUSING FOR MOVEMENT THEREWITH, A CONTACT ARM FIXED TO SAID SHAFT FOR ROTATION THEREWITH RELATIVE TO SAID RESISTANCE ELEMENT TO VARY THE EFFECTIVE LENGTH OF SAID RESISTANCE ELEMENT BETWEEN ONE END THEREOF AND SAID CONTACT ARM, A CAM HAVING A SURFACE DEFINING A PREDETERMINED CHARACTERISTIC FIXED TO SAID SHAFT FOR ROTATION THEREWITH, A SECOND ROTATABLE SHAFT, AN ARM EXTENDING FROM SAID SECOND SHAFT, A FOLLOWER CARRIED BY SAID ARM ENGAGING SAID SURFACE TO EFFECT ANGULAR DIS- 